"I simply did not have the financial resources to compete in the primary," he told The Associated Press in a telephone interview.

Wagner's exit leaves four candidates in the race for the nomination to challenge Republican Gov. Tom Corbett -- York businessman Tom Wolf, U.S. Rep. Allyson Schwartz, state Treasurer Rob McCord and former state environmental protection secretary Katie McGinty.

Wagner, 66, a former state senator from Pittsburgh who won two statewide elections as auditor general, was a latecomer to a gubernatorial campaign that began in late 2012.

After months of indecision, he tossed his hat in the ring in late February. That turned out to be less than a week before the release independent polls showing meteoric support for Wolf amid his campaign's heavy TV advertising that established him as the clear front-runner.

Wagner had been the only candidate from western Pennsylvania, a potential wild card in a field of candidates from Pennsylvania's southeastern quadrant. He acknowledged that he was likely to be outspent by opponents who had collectively raised more than $27 million last year.

"Reality hit when I started to make phone calls to raise (money) after I filed my petition," he said, noting that many of his traditional supporters were committed to another candidate or not taking sides.

A Vietnam War veteran, Wagner launched his political career as a Pittsburgh city councilman. He sought the Democratic nomination for governor in 2010 but was defeated in the primary by Allegheny County Executive Dan Onorato, who lost to Corbett.

Last year, Wagner ran for Pittsburgh mayor but was defeated in the primary.